Glow-discharge tube



Dec. 9, 1958 v G. J. M. AHSMANN 2,864,024

GLOW-DISCHARGE TUBE Filed Oct. 28. 1955 INVENTOR GERARDUS JOSEPHUS MARIE AHSMANN AGE T United States Patent GLOW-DISCHARGE TUBE Gerardus Josephus Marie Ahsmann, Eindhoven, Netherlands, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application October 28, 1955, Serial No. 543,563

Claims priority, application Netherlands November 16, 1954 1 Claim. (Cl. 313-185) This invention relates to glow discharge tubes, the cathode of which is activated by alkaline earth oxides or similar materials.

In glow discharge tubes it is often desirable to create a considerable diiference between the ignition voltage and the operating voltage. This has the advantage that, in circuit arrangements comprising such tubes, the voltage impulse which occurs on ignition of the tube, is stronger. Without considerably increasing the operating voltage the ignition voltage can be raised by increasing the spacing between the cathode and the anode or the pressure of the gas filling or both. This has a limitation in that, except in several gases and under particular conditions, an anode drop occurs which may give rise to oscillations or other unstabilities. Moreover, the anode drop involves a considerable impedance increase with regard to voice frequencies, which is particularly disadvantageous with respect to tubes for use in telephone systems.

The present invention has for its object to provide a glow discharge tube which permits the use of a higher ignition voltage without the occurrence of anode drop during operation.

In accordance with the invention in a glow discharge tube comprising a cathode activated by alkaline earth oxides or such like materials, the anode consists, at least at its surface, of gold, silver or thorium. The invention is based on the realisation that activating material from the cathode easily gives rise to electron-emission at the anode as a result of impinging photons, metastable atoms ice and possible electrons from the discharge tube. This anode-emission involves an anode drop. The anodeemission is now reduced by means of the layer of emission-counteracting material at the anode surface, by which layer the work function is maintained high.

It is known, it is true, to cover anodes and grids of vacuum discharge tubes with gold, silver or thorium in order to prevent thermal emission, but in this case neither so-called anode drop, nor independent oscillations ever occurred.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawing, given by way of example, which is a cross-section of the electrode system of an electric discharge tube in accordance with the invention.

In the drawing, the reference numeral 1 denotes a glass discharge tube and 2 denotes the cathode which consists of a nickel plate coated with barium-strontium-calcium oxide 3. Two nickel rods 4 constitute the auxiliary anodes, whilst the anode consists of a nickel tube 5 covered with a layer of gold a few microns thick. The gas filling consists of argon at a pressure of 18 mm., whilst the spacing between the cathode and the main anode is 3 mm.

If desired, silver or thorium may be substituted for gold.

What is claimed is:

A glow-discharge tube containing an inert gas filling in said tube at a pressure of about 18 mms. of mercury, a cold cathode, a layer of alkaline-earth oxides on said cathode for enhancing the emission thereof, an anode spaced from said cathode, and a layer of the element selected from the group consisting of gold, silver and thorium covering said anode for reducing the electron emission therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 2,348,045 Wooten May 2, 1944 2,479,164 Inman Aug. 16, 1949 2,524,227 Klein Oct. 3, 1950 

